This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | -8 |
| 5 | -11 |
| 6 | -19 |
| 7 | 846 |
| 8 | -1896 |
| 9 | -111 |
| 10 | -228159 |
| 11 | 2453010 |
| 12 | -11353440 |
| 13 | 173733429 |
| 14 | -3565851587 |
| 15 | 41759789358 |
| 16 | -501111404080 |
| 17 | 9579604130881 |
| 18 | -176443305192159 |
| 19 | 2870638703204994 |
| 20 | -53275482352387864 |
| 21 | 1134671091039714069 |